How to Measure a Chamber Lead

A firearm chamber is constructed to fit a specific bullet caliber. The dimensions of the chamber need to be calibrated precisely in order for the weapon to fire a specific round effectively. Older weapons or obscure models may not have the caliber size stamped on the barrel. In this case, measuring the chamber lead is the only way to know the weapon's caliber. This process can be accomplished using a casting alloy to measure the chamber dimensions.

Things You'll Need

  • Gun Vise
  • Gun oil
  • Cleaning rod and patches
  • Casting alloy
  • Side-bench vise
  • Propane torch
  • Ladel
  • Digital dial caliper
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Instructions

    • 1

      Unload the weapon completely. Visually inspect the chamber to ensure no live ammunition is present.

    • 2

      Secure the weapon in a padded gun vise. Oil the chamber with a light coat of gun oil.

    • 3

      Attach a cleaning patch to a cleaning rod. Insert the rod into the barrel, stopping the patch where the chamber and bore meet. Remove the rod.

    • 4

      Secure the weapon in a side-bench vise, muzzle pointing at the ground. If working with a rifle you also can lean the weapon against a table or bench, but this is also best done when secured properly in a vise so that the weapon doesn't fall over.

    • 5

      Melt the casting alloy into a ladle using a propane torch. Pour the alloy into the chamber until the chamber is full. Allow 30 minutes for the alloy to set and cool.

    • 6

      Secure the weapon into the padded gun vise again. Ram the rod and patch toward the buttstock to knock the casting alloy loose. Remove the casting alloy.

    • 7

      Measure the alloy base, overall length and the diameter using the digital dial caliper. Take your measurements and cross-reference using a cartridge/caliber dimension chart. The chart will tell you what the weapon's caliber is based on your measurements of the alloy.